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ERV and humidity

mbasheville | Posted in General Questions on


I moved into a new house in Asheville, NC about a year ago. The house is very well sealed and has a Venmar Kubix ERV. In the summer, though, it tends to get really humid inside the house (anywhere from 55% to 75%). Is this normal in houses with ERVs? Is there an adjustment I can make on the ERV to fix this? I’m new to the ERV concept and need some help! Thanks in advance!


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  1. ohioandy | | #1

    There's only one scenario in which ventilation can reduce humidity in your house: when the outside air has a lower ABSOLUTE humidity than the inside air. Then you can trade your damp inside air for dry outside air. That's a rare situation in an Asheville summer, I figure.

    Beyond that, an ERV can't lower humidity, it only exchanges it between the ingoing and outgoing air streams, at least preventing an INCREASE in inside relative humidity. Your air conditioning system will have a provision for duhumidification, otherwise you'll have to use a standalone dehumidfier.

  2. GBA Editor
    Martin Holladay | | #2

    You didn't tell us whether or not your house has air conditioning. If your house doesn't have air conditioning, it is totally normal for your house to be humid during the summer in North Carolina.

    The most common way that homeowners control the indoor humidity in North Carolina during the summer is by using an air conditioner.

    It's possible that you are over-ventilating. Every minute that you operate the ERV during the summer will tend to increase indoor humidity levels, unless the weather is very cool. So one way to improve your situation is to reduce your ventilation rate during the summer as much as possible.

  3. mbasheville | | #3

    Thanks for your responses. We do have air conditioning and when running it seems to bring the humidity levels down to about 50-55%. We keep it at about 73, so when it shuts off for most the the night the humidity levels go up to about 75%. We don't have any wall controls for the ERV so it seems like the only options are low ventilation, high ventilation, or off. I think it runs all the time, but I'm not sure. If this is the case, it definitely seems that this would be over-ventilating. I turned it to low ventilation yesterday, but it didn't seem to make too much of a difference. Should I turn the unit off entirely?

  4. GBA Editor
    Martin Holladay | | #4

    Low speed is probably better than high speed -- probably year round, but especially during hot, humid weather. But it's hard to know what your ventilation rate is unless your system was properly commissioned by a contractor who measured air flow.

    It may also be possible to put your ERV on a timer so that it only operates (for example) for 20 minutes out of every hour. If your house doesn't feel stuffy, and you aren't noticing any problems with air quality, you're probably getting enough fresh air.

    Finally, if your air conditioner isn't doing a good job of controlling indoor humidity, you can always buy and use a stand-alone dehumidifier. Before you do that, however, it might be a good idea to find out the source of the moisture.

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